package 强化训练;

import java.util.Scanner;

//未通过
public class day34养兔子 {
    static long[] arr = new long[90];
    public static void main(String[] args){
        fio(90);
        Scanner sc = new Scanner(System.in);
        while (sc.hasNext()){
            int n = sc.nextInt();
            System.out.println(arr[n]);
        }
    }
    public static void fio(int n){
        arr[0] = 1;
        arr[1] = 1;
        long sum = 1;
        for (int i = 2; i < arr.length; i++) {
            arr[i] = arr[i-1] + arr[i-2];
            sum = sum + arr[i];
        }
    }

}
